JPH08234590A - Image forming device - Google Patents

Abstract

PURPOSE: To surely detect a recording sheet attracted and held by a sheet carrier, and to recognize whether charge removing of the sheet carrier is surely performed or not, at an early stage, even in a case that area proportion of an image with respect to the recording sheet is large, and the image space is limited in the leading end of the recording sheet. CONSTITUTION: In this image forming device capable of forming the toner image on the image carrier corresponding to the image information, and transferring the toner image from the image carrier to the recording sheet, by rotating the sheet carrier 35 attracting and holding the recording sheet on the surface in synchronism with the image carrier, a specified sheet holding surface C for attracting the recording sheet is provided on the peripheral surface of the sheet carrier, and moreover, a low reflection ratio area 60 partially covered by the recording sheet is formed on the leading end of the sheet holding surface C. Moreover, a reflection type photosensor 39 for detecting the reflection ratio of the sheet carrier 35 including the low reflection ratio area is disposed on the peripheral surface of the sheet carrier 35, and the presence or absence of the recording sheet on the sheet holding surface C is judged based on the detection signal of the photosensor 39.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for transferring a toner image formed on an image bearing member such as a photosensitive drum onto a recording sheet to form an image, and more particularly to a sheet bearing member. The present invention relates to an image forming apparatus of a type that transfers a toner image onto a held recording sheet.

[0002]

2. Description of the Related Art As one of the methods for transferring a toner image formed on an image bearing member such as a photosensitive drum onto a recording sheet, a recording sheet is adsorbed and held by a sheet bearing member having a dielectric film attached thereto. It is known to transfer a toner image onto a recording sheet while rotating the sheet carrier and the image carrier in synchronization. In this method, since the recording sheet is electrostatically adsorbed to the dielectric film by applying an electric charge to the dielectric film, the recording sheet is conveyed and the recording sheet is separated from the latent image carrier in accordance with the transfer of the toner image. It has the advantage of being able to

Therefore, this system is suitable for a color copying machine which requires multiple transfer of toner images of a plurality of colors onto a recording sheet. In the conventional color copying machine, a sheet carrier holding the recording sheet is held by the image carrier. Black and yellow, which are sequentially formed on the image carrier by repeatedly rotating in synchronization with the body,
The cyan and magenta toner images are repeatedly transferred onto the recording sheet.

By the way, in the image forming apparatus for transferring the toner image in this manner, sheet detecting sensors are arranged at several places around the sheet carrier, and the recording sheet sucked and held by the sheet carrier. Is generally adapted to be detected appropriately. This is for detecting whether or not the recording sheet is adsorbed at a predetermined position on the sheet carrier at a predetermined timing or is peeled from the position, and the recording sheet is detected based on the detection signal of the sheet detection sensor. When the sheet conveyance error occurs, the image forming operation is stopped urgently.

As the above-mentioned sheet detecting sensor, a reflection type photo sensor having a light emitting portion and a light receiving portion has been conventionally used, and the recording sheet is detected based on the difference between the reflected light amount of the sheet carrier itself and that of the recording sheet. It is determined whether or not the sheet has passed a position facing the sheet detection sensor. FIG. 11 shows a detection signal of the sheet detection sensor that changes depending on the amount of reflected light received, and shows that the larger the output of the detection signal, the smaller the amount of reflected light. Speaking of the specific detection of the recording sheet, it is made by checking whether the output of the detection signal is larger than a predetermined threshold value, and when the leading edge of the white plain recording sheet passes the facing position of the sheet detection sensor. The output of the detection signal changes across the threshold value, and the recording sheet is detected.

[0006]

However, in the conventional image forming apparatus for detecting the recording sheet on the sheet carrier in this manner, the area ratio of the toner image transferred to the recording sheet is extremely large and the recording sheet is When the image margin formed at the leading end of the recording sheet is extremely narrow, as shown in FIG. 12, the amount of reflected light at the leading end of the recording sheet is small and the difference from that of the sheet carrier is small, so that the leading edge of the recording sheet is There is a problem that it is not possible to accurately detect whether or not the sheet has passed the facing position of the sheet detection sensor. In particular, in color copiers, solid images such as photographs and pictures are often copied. In such cases, if the image margin is set to be small in order to improve the appearance of the copied image, several colors of toner image will be recorded on the recording sheet. There is a problem that the recording sheet cannot be detected at the time of transfer to the sheet.

Further, when the OHP film is used as the recording sheet, the irradiation light of the photosensor is transmitted through the OHP film and reflected by the sheet carrier, and the recording sheet is detected from the detection signal of the photosensor. Since it is impossible to do so, the image forming apparatus configured as described above has conventionally used the OHP film having the tip thereof painted white. However, since the area of the white coating is narrow, it is difficult for the conventional image forming apparatus to accurately detect whether or not the OHP film is adsorbed on the sheet carrier.

On the other hand, in the above-mentioned image forming apparatus in which the recording sheet is electrostatically adsorbed to the sheet carrier, the image is prevented from being attracted to the sheet carrier and the toner image is not transferred to the recording sheet. It is necessary to eliminate the residual electric charge of the sheet carrier each time the forming operation is completed, and this is done by providing a charge eliminating corotron around the sheet carrier.

However, whether or not the static eliminator corotron is fully functioning can be recognized unless the recording sheet adsorption error or the toner image transfer failure actually occurs, and in the conventional image forming apparatus. Such trouble could not be prevented in advance.

The present invention has been made in view of the above problems, and an object of the present invention is even when the area ratio of an image to a recording sheet is large and the image margin at the leading end of the recording sheet is small. An object of the present invention is to provide an image forming apparatus capable of reliably detecting a recording sheet sucked and held by a sheet carrier.

Another object of the present invention is to quickly recognize whether or not static elimination of the sheet carrier is being carried out, so that a recording sheet adsorption error or toner image transfer failure can be prevented. An object of the present invention is to provide an image forming apparatus capable of preventing the above.

[0012]

In order to achieve the above object, the image forming apparatus of the present invention forms a toner image according to image information on an image bearing member and adsorbs and holds a recording sheet on the surface thereof. In an image forming apparatus that rotates a sheet carrier in synchronization with the image carrier and transfers the toner image from the image carrier to a recording sheet, the peripheral surface of the sheet carrier is
Forming a low reflectance region exposed from the front or rear end of the recording sheet adsorbed to the sheet carrier, and the reflectance of the sheet carrier including the low reflectance region around the sheet carrier. A reflective photo sensor for detection is provided,
The presence or absence of the recording sheet on the sheet holding surface is determined based on the detection signal of the photo sensor (Claim 1).

According to such technical means,
Even when the image margin at the tip of the recording sheet adsorbed to the sheet carrier is narrow, since the low reflectance region formed on the peripheral surface of the sheet carrier is exposed from the tip of the recording sheet, When the difference between the amount of reflected light in the image margin and that in the low reflectance region increases, and the leading edge of the recording sheet passes the position facing the photo sensor, the detection signal of the photo sensor changes significantly. This makes it possible to reliably detect the recording sheet adsorbed on the sheet carrier. Further, by applying this technique to the rear end of the recording sheet, the recording sheet adsorbed on the sheet carrier can be detected in the same manner.

As the low reflectance region formed on the sheet carrier, it is necessary that the amount of reflected light with respect to the irradiation light of the photosensor is at least smaller than that of the other regions of the sheet carrier, and the color thereof is that of the photosensor. The design may be changed appropriately according to the wavelength of the irradiation light. Further, the low reflectance region may be formed by printing on the sheet carrier, or may be formed by attaching another member to the sheet carrier.

The low reflectance region may be exposed from the front end or the rear end of the recording sheet in a state where the recording sheet is adsorbed on the sheet carrier, and the front end or the rear end does not overlap with the recording sheet. It may be continuous with the edge. However, in such a case, if an error occurs in the suction position of the recording sheet with respect to the sheet carrier, a gap is created between the low reflectance region and the leading edge or the trailing edge of the recording sheet. It may be difficult to detect. Therefore, from this point of view, it is preferable that a part of the low reflectance region is covered with the recording sheet adsorbed to the sheet carrier.

Further, in order to surely detect the low reflectance region by the photosensor, at least the width and the length of the low reflectance region exposed from the recording sheet are at least emitted from the photosensor. It is preferable to make it larger than the spot diameter (claim 3).

Further, in the case of detecting the leading edge of the recording sheet, a sheet holding surface is provided on the peripheral surface of the sheet carrier to which the recording sheets of various sizes are attracted by matching the leading edge thereof.
It is preferable to form the low reflectance region at the tip of the sheet holding surface. By doing so, it is possible to deal with recording sheets of various sizes by providing only one low reflectance region (claim 4).

Further, in order to ensure that the recording sheet can be detected even when the margin amount of the recording sheet is extremely small, the reflectance of the light beam of the photosensor due to the low reflectance region is recorded on the recording sheet. It is preferable to keep the reflectance lower than the reflectance of the toner image transferred to (5).

On the other hand, by using this low reflectance region, it is possible to detect whether or not the charge removal of the sheet carrier is completely performed. That is, when the electrical resistance value of the low reflectance region is set to be different from the other regions of the sheet carrier,
When the charge removal of the sheet carrier is not completely performed, these regions show different surface potentials, so that the charge removal failure of the sheet carrier can be detected from the difference in the surface potential. (Claim 6).

As a specific method for detecting the difference in surface potential between the low reflectance region and the other regions, an electrometer is provided around the sheet carrier, and the sheet carrier including the low reflectance region is provided. It is possible to directly detect the surface potential of the (Claim 7). By doing this, when there is a potential difference of a predetermined value or more between the surface potential of the low reflectance region and the surface potential of other regions, it is determined that the charge removal of the sheet carrier is incomplete. be able to.

As another method, a toner image is transferred to an area on the sheet carrier including at least the low reflectance area, and an image corresponding to the low reflectance area in the transferred toner image. It is also possible to detect the difference in surface potential by comparing the densities of the portions with the densities of the image portions corresponding to the other areas (claim 8). When there is a surface potential difference between the low reflectance region and the other region, the transfer efficiency of the toner image differs in each region, and it is possible to recognize the presence of the surface potential difference from the density of the transferred toner image. Because you can.

As a method of comparing the density differences of the toner images, the user himself / herself may observe the recorded image formed on the recording sheet in a normal image forming operation, and the judgment may be made based on the observation result. . Further, the toner image of the same pattern is experimentally transferred to each of the low reflectance area and the other area on the sheet carrier, and the toner image is detected by the photo sensor to determine the density difference based on the detection signal. It may be done.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The image forming apparatus of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows a first embodiment of a color copying machine to which the present invention is applied. In the figure, reference numeral 20 is a photosensitive drum, 21 is a photosensitive drum 20.
, 22 is an exposure scanning system for writing an electrostatic latent image on the photosensitive drum 20 charged by the charging corotron 21, and 23 is black (B), cyan (C), magenta (M). ) And four developing devices 23B, 23C, 23M for accommodating the yellow (Y) toner images, respectively.
23Y is a rotary developing unit which is rotatably disposed and is appropriately switched and selected; 24 is a pre-transfer corotron for removing the potential on the photoconductor drum 20; 25 is the photoconductor drum 2;
A cleaner for removing the residual toner on 0 and an erase lamp for removing the residual charge on the photosensitive drum 20.

In this embodiment, the exposure scanning system 22 is
The exposure lamp 223 that illuminates the original 222 set on the platen 221, and the exposure lamp 223 to the original 222.
A carriage 224 that moves over the area, a reflection mirror 225 that guides a beam from the surface of the original 222 by the exposure lamp 223 along a predetermined path, and a color that converts the beam from the surface of the original 222 into a digital signal for each color component. An image sensor 226, an image forming lens 227 for forming an image of a beam from the surface of the original 222 on the color image sensor 226, and a laser beam of the photosensitive drum 20 based on the image signal of each color component captured by the image sensor 226. It is configured with a laser scanning unit 228 which irradiates along the main scanning direction. The laser scanning unit 228 includes a semiconductor laser 228a and a semiconductor laser 228.
A polygon mirror 228b for diverting and deflecting the beam from a toward the main scanning direction of the photosensitive drum 20, an imaging lens 228c for forming an image of the beam from the semiconductor laser 228a along a line in the main scanning direction of the photosensitive drum 20, and It is composed of a reflecting mirror 228d that regulates the beam path.

The reference numeral 31 indicates that the recording sheet 30 is wound around and held on the peripheral surface, and the photosensitive drum 2 is attached to the recording sheet 30.
This is a transfer drum that sequentially multiple-transfers toner images of respective color components on 0. As shown in FIGS. 2 and 3, this transfer drum 3
1 is a drum frame 32 in which a pair of ring bodies 33 are connected to each other by a tie bar 34, and a drum sheet 35 made of polyvinylidene fluoride or the like is stretched through a fixing member 36. The recording sheet 30 is electrostatically attracted by being charged.

Further, an adjuster plate 37 for preventing the drooping of the drum sheet 35 is disposed at a portion adjacent to the tie bar 34 in the counter-rotational direction, and an electric charge is applied to the drum sheet 35 in the adjuster plate 37. A through hole 38 for giving is formed like a ladder.

Further, as shown in FIGS. 1 and 2, the transfer drum 31 has an adsorbing corotron 41 for charging the drum sheet 35 when the recording sheet 30 is held, and a toner image on the photosensitive drum 20 for recording the recording sheet 30. A transfer corotron 42 for transferring to the side, a static charge corotron 43 for neutralizing the recording sheet 30 after the final color transfer process, and a cleaning static charge corotron 44 for removing charges on the drum sheet 35 after the final color transfer process. The cleaning brush 45 that cleans paper dust and the like adhering to the drum sheet 35 after the transfer process of the final color, the inner push roll 46 that pushes up the drum sheet 35 from the inside when the recording sheet 30 is peeled off, and the recording sheet 30 Peeling finger 4 for peeling
7 are provided. Reference numeral 48 is a sheet conveying system that conveys the recording sheet 30 supplied from a sheet feeding cassette (not shown) to the suction corotron 41 portion at a predetermined timing according to each mode.

Further, at several places around the transfer drum 31, the recording sheet 3 adsorbed and held on the transfer drum 31 is held.
A sheet detection sensor 39 for detecting 0 is provided. The sheet detection sensor 39 is a reflection type photo sensor that is mainly composed of a light emitting section that irradiates infrared light and a light receiving section that detects infrared light reflected by the transfer drum 31, and the sheet type detection sensor 39 of the adsorption corotron 41. Downstream side, transfer corotron 42
Are provided at three locations on the downstream side and on the downstream side of the peeling finger 47. These sheet detection sensors 39 are time-divisionally driven at the timing synchronized with the rotation reference signal of the transfer drum 31, and the recording sheet 3 held by the transfer drum 31.
This is detected when the leading edge of 0 passes the facing position of each sheet detection sensor.

Further, reference numeral 50 is a fixing device for inserting the recording sheet 30 after the transfer process and fixing the unfixed toner image on the recording sheet 30. In this embodiment, a heating device having a heater incorporated therein is used. The recording sheet 30 from the transfer drum 31 is conveyed to the fixing device 50 via the guide plate 53. The recording sheet 30 is composed of a roll 51 and a pressure roll 52 arranged in pressure contact with the heating roll 51. Further, reference numeral 54 is a fuser outlet roll that conveys the recording sheet 30 that has passed through the fixing device 50, and 55 is the fixing device 50.
The fuser outlet switch for detecting the trailing edge of the recording sheet 30 that has passed through the recording sheet 30, 56 is a discharge tray in which the fixed recording sheet 30 is accommodated, and 57 is a discharge tray 56.
Is an exit roll for sending out.

In the color copying machine configured as described above, first, when the user operates the copy start switch, the original 222 is scanned and the photosensitive drum 20 is scanned.
An electrostatic latent image corresponding to black K is written on the top. On the other hand, in the rotary developing unit 23, the black developing device 23K is set at a position facing the photoconductor drum 20, and the electrostatic latent image is developed by the black developing device 23K with a slight delay from the writing timing. Then, the black K toner image thus formed is transferred to the recording sheet 30 held on the transfer drum 31. Further, when the developing process by the black developing device 23K is completed, the developing device is replaced until the transfer drum 31 completes one rotation cycle, and the yellow developing device 23Y is exposed by the 90 ° rotation of the rotary developing unit 23. It is set at a position facing the body drum 20.

After that, these operations are repeated every one rotation cycle of the transfer drum 31, and the toner images of yellow Y, magenta M, and cyan C are held from the photosensitive drum 20 to the transfer drum 31 each time. The image is transferred to the recording sheet 30, and a superposed toner image is formed on the recording sheet 30 by four color toner images. Then, the recording sheet 30 on which the cyan C toner image has been transferred is peeled off from the transfer drum 31 as it is, passes through the fixing device 50, and then the discharge tray 56.
Is discharged to.

In the color copying machine of the present embodiment in which image formation is performed in this manner, the suction position of the recording sheet on the transfer drum 31 is selectively used according to the size and type of the recording sheet 30. There is. First, FIG.
As shown in FIG. 5, sheet holding surfaces A and B are set on the peripheral surface of the transfer drum 31, and two recording sheets at a time are provided for recording sheets of JIS standard A4 size or smaller or letter size recording sheets. The sheets 30 and 30 are held on the sheet holding surfaces A and B, respectively. At this time, the tip reference P _A of the sheet holding surface _A is the tie bar 34.
Is a position on the adjuster plate 37 that is slightly displaced downstream in the rotation direction from 180 ° from the tip reference P _A.
The deviated line serves as the front end reference P _B of the sheet holding surface B. Further, recording sheets of other sizes are held in the sheet holding surface A or the area S extending from the sheet holding surface A to the sheet holding surface B.

However, the tip reference P of the sheet holding surface A is
_A is overlapped with the adjuster plate 37, and it is difficult for the adsorption corotron 41 to give a sufficient charge to the back side of the drum sheet 35 with respect to the front end reference P _A. Therefore, a stiff recording sheet such as OHP film or thick paper is used. When 30 is held on the sheet holding surface A, there is a concern that the leading end of the recording sheet 30 may be separated from the drum sheet 35. Therefore, in this embodiment, the sheet holding surface C is set at a position slightly displaced rearward from the sheet holding surface A, and the recording sheet 30 such as an OHP film or thick paper is held on the sheet holding surface C. ing. Therefore, this sheet holding surface C
The tip reference P _C is a position that does not overlap with the adjuster plate 37.

For the same reason, the sheet holding surface A
If the recording sheet 30 is held by the recording sheet 3,
Since it is difficult for the transfer corotron 42 to apply sufficient charges to the leading edge of 0, when a copy is performed using the sheet holding surface A for an original having a small image margin, there is a concern that an image may be missing at the leading edge of the recording sheet 30. is there. Therefore, in the color copying machine of the present embodiment, the user arbitrarily sets the sheet holding surface C
A margin erasing amount reduction mode capable of selecting is provided, and the recording sheet 30 is held on the sheet holding surface C when copying a document such as a photograph or a picture whose image margin is desired to be reduced. .

Of the recording sheets 30 held on these sheet holding surfaces, the recording sheets 30 on the sheet holding surfaces A and B are detected when the recording sheet 30 passes the position where the sheet detection sensor 39 faces. Sensor 3
Since the output signal of 9 changes as shown in FIG.
The / N ratio can be increased. Therefore, it is possible to determine whether the leading edge of the recording sheet 30 has passed by setting an appropriate threshold value and checking whether the output of the sheet detection sensor 39 changes across the threshold value.

However, among the recording sheets 30 held on the sheet holding surface C, the recording sheet 30 relating to the edge erasing amount reduction mode, that is, the recording sheet in which the image margin at the front end after the toner image is transferred is suppressed to be small. With respect to No. 30, since the output signal of each sheet detection sensor 39 changes with a small S / N ratio as shown in FIG. 9, it is difficult to detect this.

Therefore, in this embodiment, as shown in the development view of the drum sheet 35 shown in FIG. 5, on the drum sheet 35 corresponding to the front end reference P _C of the sheet holding surface C and facing the sheet detection sensor 39. When the low reflectance region 60 is printed on the sheet and the recording sheet 30 is held on the sheet holding surface C, a part of the low reflectance region 60 is covered with the recording sheet 30. The low reflectance region 60 is formed in black so as to easily absorb the infrared light emitted by the sheet detection sensor 39.

Further, the low reflectance region 60 largely projects in the rotational direction of the transfer drum 31 from the front end reference P _{C of} the sheet holding surface C, and from below the recording sheet 30 held on the sheet holding surface C. The size of the exposed portion is set to be larger than the spot diameter of the light beam emitted by the sheet detection sensor 39 in both the length (circumferential direction of the transfer drum 31) and the width (axial direction of the transfer drum 31). .

As a result, when the recording sheet 30 relating to the edge erasing amount reduction mode is held on the sheet holding surface C, the output of the detection signal of the sheet detection sensor 39 changes as shown in FIG. That is, since the output of the detection signal corresponding to the low reflectance area 60 is larger than the output of the detection signal of the drum sheet 35 itself, the output of the detection signal corresponding to the low reflectance area 60 and the image of the leading edge of the recording sheet 30. The S / N ratio with that corresponding to the margin can be increased,
By using an appropriate threshold value, the leading edge of the recording sheet 30 can be reliably detected. By forming the low reflectance region 60 on the drum sheet 35 in this embodiment, even if the image margin at the leading edge of the recording sheet 30 is suppressed to 4 mm, the leading edge of the recording sheet 30 is detected by the sheet detection sensor 39.
Could be detected.

The low reflectance region 60 also exhibits the same effect when a copy job is performed with the OHP film held on the sheet holding surface C. Since the drum sheet 35 itself is transparent when the OHP film is held on the sheet holding surface C, even when a white painted portion imitating the image margin of plain paper is formed at the tip of the OHP film, Although the S / N ratio of the output of the sheet detection sensor 39 is inevitably small, it is necessary to cover a part of the low reflectance region 60 provided on the drum sheet 35 with the tip of the OHP film as described above. For example, the S / N ratio of the detection signal between the white coating portion and the low reflectance region 60 can be increased, and the tip of the OHP film can be surely detected.

As shown in FIG. 5, the low reflectance region 61 printed in black is formed on both ends of the drum sheet 35. In the low reflectance region 61, the tie bar 34 and the adjuster plate 37 are formed on the drum sheet. The sheet detection sensor 39 prevents the tie-bar 34 and the adjuster plate 37 from being mistakenly determined to be the recording sheet 30.

Further, in this embodiment, the low reflectance regions 60 and 6 are provided corresponding to the front end references P _A and P _C of the sheet holding surfaces A and C.
1 is formed, but the remaining sheet holding surface B
A low reflectance region may be formed with respect to the tip reference P _B. By doing so, the recording sheets held on the sheet holding surfaces A, B, and C can be reliably detected. Further, in such a case, as shown in FIG. 7, the low reflectance region 60 can be formed in a band shape along the circumferential direction of the transfer drum 31.

Next, a second embodiment of the present invention will be described. In this embodiment, the drum sheet 35 is used in the first embodiment.
Utilizing the low reflectance region 60 formed above, the cleaning static elimination corotron 4 disposed around the transfer drum 31.
It is to check whether 4 is fully functional.

That is, when the low reflectance region 60 is printed or attached on the drum sheet 35, the electric resistance value of the low reflectance region 60 is determined by the other regions (hereinafter,
It becomes different from the electric resistance value of the peripheral area). If the cleaning charge-eliminating corotron 44 is fully functioning, the surface potential of the drum sheet 35 that has been discharged by the cleaning charge-eliminating corotron 44 is uniform, and there is a potential difference between the low reflectance region 60 and the peripheral region. Should not. However, cleaning static elimination Corotron 44
If the function is incomplete, a potential difference of a predetermined value or more remains between the low reflectance region 60 having a different electric resistance value and the peripheral region.

Therefore, by disposing an electrometer around the transfer drum 31 and at a position facing the low reflectance region, and measuring the potential difference between the low reflectance region 60 and the peripheral region, the cleaning static elimination corotron 44 is provided. You can check whether it is fully functional. 8. FIG. 8 is a flowchart showing a specific procedure for finding a failure of the cleaning static elimination corotron 44 by this method.

When a potential difference remains between the low reflectance region 60 and the peripheral region, even if the back side of the drum sheet 35 is uniformly charged by the transfer corotron 42,
The electric field strength that contributes to the transfer of the toner image is the low reflectance region 60.
And the surrounding area will be different. Therefore, when the cleaning charge-eliminating corotron 44 is not completely functioning, the transfer efficiency of the toner image in the low reflectance area 60 is different from that in the peripheral area, and the electrical resistance value of the low reflectance area 60 is reduced. When the toner image transferred to the recording sheet 30 is set to be larger than that of the peripheral area, a white spot 625 corresponding to the low reflectance area 60 occurs as shown in FIG. Further, the image density of the portion corresponding to the low reflectance region 60 is lower than that of the peripheral region, even if the white spot does not occur.

In the color copying machine of this embodiment, the recording sheet 30 held on the sheet holding surface A of the transfer drum 31 completely covers the low reflectance region 60 formed at the tip of the sheet holding surface C. When a copy job is performed using the sheet holding surface A, the low reflectance region 6 of the copied recorded image
By confirming whether the toner image transfer unevenness or white spots does not occur at the position corresponding to 0, it is possible to confirm whether the cleaning charge-eliminating corotron 44 is fully functioning.

Further, a system for forming a toner image of a specific pattern (hereinafter referred to as a reference patch) on the photosensitive drum 20 on a trial basis, measuring the density of the reference patch, and controlling the image density based on the measurement result is provided. In the copier provided, it is possible to confirm whether the drum sheet 35 is sufficiently discharged by using this system. That is, the reference patches are continuously formed on the photoconductor drum 20, and are transferred to the low reflectance region 60 of the transfer drum 31 and the peripheral region thereof, and the reference patches transferred to the low reflectance region 60 are transferred. The difference between the density and the density transferred to the peripheral area may be measured by a photosensor arranged around the transfer drum 31. According to such a configuration, it is possible to confirm whether or not the cleaning charge removal corotron 44 is fully functioning based on the detection signal of the photosensor, and when it is determined that the charge removal of the drum sheet is incomplete. Can be displayed on the operation panel of the copying machine to prohibit subsequent copy jobs. Note that FIG. 10 is a flowchart showing a specific procedure for finding a failure of the cleaning static elimination corotron 44 by this method.

Further, in this color copying machine, by transferring the test pattern image having gradation to the transfer drum 31, the transfer corotron 42 or the pre-transfer corotron 24 can fully function during the image forming operation. It can be determined whether or not. For example, if the transfer corotron 42 does not apply a predetermined charge amount to the back surface side of the drum sheet 35, the electric field strength at the time of transferring the toner image from the photosensitive drum 20 side to the transfer drum 31 side will be insufficient. , Recording sheet 3 with a toner image having a certain density or more
It becomes impossible to transfer to 0. Therefore, when the transfer corotron 42 is not completely functioning, a test pattern image having gradation is provided on the drum sheet 3 of the transfer drum 31.
5 or transfer to the recording sheet 30 held by this,
Since the gradation is not expressed for toner images having a certain density or higher, it is possible to judge the failure of the transfer corotron 42 based on the density of the test pattern image transferred to the transfer drum 31 side.

On the other hand, if the transfer pretreatment corotron 24 is not fully functioning and the amount of charge given to the toner image formed on the photosensitive drum 20 is insufficient, the charge amount of the toner image is set as a transfer condition. Therefore, even if the transfer corotron 42 described above is fully functional, it is impossible to transfer a toner image having a certain density or higher onto the recording sheet 30. Therefore,
Pre-Transfer Processing When the corotron 24 is not completely functioning, a test pattern image having gradation is transferred to the transfer drum 31.
Drum sheet 35 or recording sheet 3 held by the drum sheet 35
When it is transferred to 0, the gradation is not expressed even for the toner image having a certain density or more, so that the failure of the pre-transfer processing corotron 42 is judged based on the density of the test pattern image transferred to the transfer drum 31 side. can do.

As a method of confirming the density of the test pattern image transferred to the transfer drum 31 side, the drum sheet 3
The density of the test pattern image transferred to the transfer drum 3
It may be detected by a photo sensor arranged around 1.
When the output of the photo sensor does not change stepwise in correspondence with the gradation of the test pattern image, the transfer corotron 42
Alternatively, it can be determined that the pre-transfer processing corotron 24 is out of order.

As a method of transferring the test pattern image having gradation to the transfer drum 31 side, a toner image having gradation may be formed on the photosensitive drum 20 from the beginning. Alternatively, a toner image having a uniform density may be formed on the photoconductor drum 20, and the output of the transfer corotron 42 may be changed stepwise at the time of transfer to give gradation to the toner image.

Further, by transferring the test pattern image having the above gradation to the recording sheet and outputting it from the copying machine,
It is also possible to confirm whether or not the static elimination corotron 43 is fully functioning. That is, the static elimination corotron 43
If the recording sheet is not completely functioning, when the recording sheet is separated from the transfer drum 31, streaky image disturbance occurs in the intermediate gradation portion of the toner image transferred to the recording sheet. This phenomenon occurs in the toner image of the final color in the case of forming a color image by multiple-transferring the toner images of four colors as in the copying machine of No. 3, so confirm the phenomenon from the output test pattern image. For example, it is possible to confirm whether the static elimination corotron 43 is fully functional.

However, this phenomenon is unlikely to occur in the high density portion and the low density portion of the toner image, and the density of the intermediate gradation portion depends on the environmental conditions such as temperature and humidity at that time. Therefore, if the test pattern image having a constant density is transferred to the recording sheet, it is expected that such a phenomenon does not occur even though the static elimination corotron 43 is not completely functioning. Therefore, the test pattern image transferred to the recording sheet in order to confirm the function of the static eliminator corotron 43 needs to have continuous gradation or multi-step gradation from high density to low density.

[0055]

As described above, according to the color image forming apparatus of the present invention, the low reflectance region which is partially covered by the recording sheet is formed at the tip of the sheet holding surface provided on the sheet carrier. Then, when the leading edge of the recording sheet held by the sheet carrier passes the facing position of the photo sensor,
Since the detection signal of the photo sensor is changed greatly, even when the image area ratio to the recording sheet is large and the image margin at the leading edge of the recording sheet is small,
It is possible to reliably detect the recording sheet sucked and held by the sheet carrier.

Further, by making the electric resistance value of the low reflectance region different from that of the other regions of the sheet carrier, when the static elimination of the sheet carrier is not complete, the difference in surface potential between these regions is Therefore, it can be recognized at an early stage whether or not the sheet carrier is surely discharged, and it is possible to prevent a recording sheet suction error or a toner image transfer failure.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of a color copying machine to which the present invention is applied.

FIG. 2 is a schematic configuration diagram showing a transfer drum and its peripheral devices.

FIG. 3 is an enlarged view showing the vicinity of a tie bar of a transfer drum.

FIG. 4 is a diagram showing a region of a sheet holding surface of a transfer drum.

FIG. 5 is a development view of a drum sheet of a transfer drum.

FIG. 6 is a graph showing an output corresponding to the sheet holding surface C of the sheet detection sensor.

FIG. 7 is a development view showing another example of the drum sheet of the transfer drum.

FIG. 8 is a flowchart showing a procedure for detecting a charge removal failure of a transfer drum with an electrometer.

FIG. 9 is a diagram showing a state in which white spots corresponding to a low reflectance region occur in a formed copy image.

FIG. 10 is a flowchart showing a procedure for detecting a charge removal defect of a transfer drum by a photo sensor.

FIG. 11 is a graph showing the output of the sheet detection sensor when a white plain recording sheet is detected.

FIG. 12 is a graph showing the output of the sheet detection sensor when the image margin at the leading edge of the recording sheet is small.

[Explanation of symbols]

20 ... Photosensitive drum (image bearing member), 30 ... Recording sheet,
31 ... Transfer drum (sheet carrier), 39 ... Sheet detection sensor (photo sensor), 60 ... Low reflectance region

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaaki Tokunaga 2274 Hongo, Ebina City, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd.

Claims (10)

[Claims] 1. A toner image according to image information is formed on an image carrier, and a sheet carrier having a recording sheet adsorbed and held on its surface is rotated in synchronization with the image carrier to form the toner image on the image carrier. In the image forming apparatus for transferring from the recording sheet to the recording sheet, a low reflectance region exposed from the front or rear end of the recording sheet adsorbed to the sheet supporting body is formed on the peripheral surface of the sheet supporting body, and A reflection type photosensor for detecting the reflectance of the sheet carrier including the low reflectance area is provided around the carrier, and the presence or absence of the recording sheet on the sheet holding surface based on the detection signal of the photosensor. An image forming apparatus, characterized in that 2. The image forming apparatus according to claim 1, wherein the low reflectance region formed on the sheet carrier is partially covered with the recording sheet adsorbed on the sheet carrier. 3. In the low reflectance region, both the width and the length of the portion exposed from the recording sheet adsorbed to the sheet carrier are larger than the spot diameter of the light beam emitted by the photosensor. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. 4. A sheet holding surface is provided on the peripheral surface of the sheet carrier for adsorbing recording sheets of various sizes with their leading ends aligned, and the low reflectance region is formed at the leading end of the sheet holding surface. The image forming apparatus according to claim 1, wherein: 5. The image forming apparatus, wherein the reflectance of the light beam emitted by the photosensor in the low reflectance region is lower than the reflectance of the toner image transferred onto the recording sheet. 6. The electrical resistance value of the low reflectance region is made different from the electrical resistance values of the other regions of the sheet carrier, and a defect of static elimination of the sheet carrier is detected from the difference in surface potential of these regions. The image forming apparatus according to claim 1, wherein: 7. An electrometer for detecting the surface potential of the sheet carrier including the low reflectance region is provided around the sheet carrier, and the sheet carrier of the sheet carrier is detected based on a detection signal of the electrometer. The image forming apparatus according to claim 6, wherein a defect in charge removal is detected. 8. A toner image is transferred to an area on the sheet carrying body including at least the low reflectance area, and a charge removal failure of the sheet carrying body is detected based on the density of the transferred toner image. The image forming apparatus according to claim 6, which is characterized in that. 9. A toner image according to image information is formed on an image carrier, and a sheet carrier having a recording sheet adsorbed and held on its surface is rotated in synchronization with the image carrier to form on the image carrier. An image forming apparatus for transferring the toner image from the image carrier to a recording sheet by a transfer charger arranged on the back side of the sheet carrier after adjusting the charge amount of the formed toner image by a pre-transfer charger. An image characterized by transferring a toner image having gradation to the sheet carrier and detecting a malfunction of the pre-transfer charger or the transfer charger based on the density of the toner image after the transfer. Forming equipment. 10. A toner image according to image information is formed on an image carrier, and a sheet carrier having a recording sheet adsorbed and held on the surface thereof is rotated in synchronization with the image carrier to form the toner image on the image carrier. In the image forming apparatus, which transfers the recording sheet to the recording sheet and then removes the recording sheet from the sheet carrier while removing the charge by the peeling auxiliary static eliminator, the toner image having gradation is transferred to the recording sheet. An image forming apparatus, wherein a recording sheet is peeled from a sheet carrier, and an operation failure of the peeling auxiliary static eliminator is detected based on a state of a toner image carried on the recording sheet after peeling.